dt-bindings: brcmstb-gpio: document properties for wakeup

Some brcmstb GPIO controllers can be used to wake from suspend, so use
the de facto standard property 'wakeup-source' to mark the nodes of
controllers with that capability.

Also document interrupts-extended, which will be used for wakeup
handling because the interrupt parent for the wake IRQ is different
from the regular IRQ.

While we're at it, a few more fixes: We don't actually use the
"interrupt-names" property, so remove it from the listed optional
properties and from the examples.  And since we're modifying the
examples, also follow Brian's suggestions to:
- change #gpio-cells, #interrupt-cells, and brcm,gpio-bank-widths from
  hex to dec
- use phandles

Reviewed-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Gregory Fong <gregory.0xf0@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>